Maria Sharapova Tennis: ISTANBUL Maria Sharapova

ISTANBUL: It was not Sam Stosur's most spectacular victory in some respects, but it was among her most satisfying in terms of how, where and, especially, who. So significant was Stosur's first defeat of her nemesis Maria Sharapova in 10 attempts that it was rated by her coach David Taylor as among the best five wins in the US Open champion's career.

''I think it's definitely up there with one of my probably best victories,'' agreed Stosur, after beating the world No. 2, 6-1, 7-5 on the opening night of the year-end WTA Championships. ''It's hard to rate things in order, but definitely one of my more pleasing ones, and being at the championships and getting off to a good start is also a nice thing, as well.''

Stosur had won just two sets in her previous nine matches against Sharapova, the triple grand slam winner who had been sidelined for a month with an ankle injury and found her movement compromised against an opponent whose court coverage has improved at a similar rate as her composure and mental resilience.

Maria Sharapova

Maria Sharapova

After a dour but important opening service hold morphed into an emphatic first set, the Australian stayed composed when down 0-3 in the second, and again when facing three break points in the final game, as she defended well and played smart, relying more on her placement and slice than her big kicking serve and jumping forehand.

''I would think with the conditions and the court, it's not conducive to doing that,'' she said. ''That's probably why I am so pleased with that win … because I couldn't use my best weapons really out there but managed to do other things with them and got a straight-sets win over somebody I've never beaten before.''

The mental barrier was imposing, as the tall Russian is one of a handful of powerful, flat hitters - Victoria Azarenka, Kim Clijsters, Venus Williams among them - who Stosur has struggled to counter, while experiencing far fewer troubles with the counter-punchers who allow her more time to play her topspin-heavy game.

Conceding her limited preparation and weakened mobility as less than ideal, Sharapova acknowledged Stosur's superior start and effectiveness of her low backhand slice. Tellingly, the woman who is statistically the best returner of the season did not get a break point until the second set. ''She just played really solid … and moved extremely well around the court and made me hit another ball,'' Sharapova said.

Taylor believed the match was won in the first 10 minutes describing as ''unbelievable'' Stosur's improvement and ability to stay close to the baseline against Sharapova's groundstrokes.

''You can see the stature of the two girls is way different, and normally Sam retreats a little bit, and therefore gives Maria more time to hurt her. So the closer she is to the line, the quicker the tempo, the more in favour of Sam, and it's not easy to do against such an amazing ball striker like Maria,'' he said. ''Look, she's two in the world and had a great year, and for Sam to do that was just fantastic.

''She hit intelligently placed serves, she sliced very well, she used the conditions - not just 'they were favourable to her, so she won,' she actually had to adapt, and I think that's something that's been missing.''

In a curious scheduling decision, Stosur had to return 15 hours later to play her second round-robin match against fourth seed Azarenka, who had not played previously.

The other day-one winners were Wimbledon champion Petra Kvitova, who celebrated her championships debut with a 6-2, 6-4 defeat of Russian sixth seed Vera Zvonareva, and world No. 1 Caroline Wozniacki, who dropped the first set 7-5 to final qualifier Agnieszka Radwanska, but recovered to win the next two 6-2, 6-4.